Development of high-power-density gear transmissions is heavily relying on advanced gear and bearing materials development, as the requirement for further power density improvement is beyond the capability of gear design engineering itself. Recently Ni—Co secondary hardening steels have shown great potential for next generation gear and bearing applications due to their great combination of strength and toughness and superior fatigue performance. More specifically, in Gear Industry Vision for 2025, it was specified that an advanced gear steel with surface hardness of 70 Rc is desired for the improvement of the power density by 25% every five years
A new generation of high performance steels, including Ferrium® C61 and C67 steel families (see U.S. Pat. No. 6,176,946 B1) has been developed. C61 steel has been proven to exceed AISI 9310 in fatigue performance and has been commercialized. The development of C67 steel is still ongoing. U.S. Pat. No. 6,176,946 B1 describes a family of case hardenable, secondary hardening steels that can achieve a high case hardness and superior core strength and toughness without the formation of primary carbides in a Ni—Co—Fe lath martensitic matrix.